8.11. pprint — Data pretty printer

Source code: Lib/pprint.py


The pprint module provides a capability to “pretty-print” arbitrary Python data structures in a form which can be used as input to the interpreter. If the formatted structures include objects which are not fundamental Python types, the representation may not be loadable. This may be the case if objects such as files, sockets or classes are included, as well as many other objects which are not representable as Python literals.

The formatted representation keeps objects on a single line if it can, and breaks them onto multiple lines if they don’t fit within the allowed width. Construct PrettyPrinter objects explicitly if you need to adjust the width constraint.

Dictionaries are sorted by key before the display is computed.

The pprint module defines one class:

class pprint.PrettyPrinter(indent=1, width=80, depth=None, stream=None, *, compact=False)

Construct a PrettyPrinter instance. This constructor understands several keyword parameters. An output stream may be set using the stream keyword; the only method used on the stream object is the file protocol’s write() method. If not specified, the PrettyPrinter adopts sys.stdout. The amount of indentation added for each recursive level is specified by indent; the default is one. Other values can cause output to look a little odd, but can make nesting easier to spot. The number of levels which may be printed is controlled by depth; if the data structure being printed is too deep, the next contained level is replaced by .... By default, there is no constraint on the depth of the objects being formatted. The desired output width is constrained using the width parameter; the default is 80 characters. If a structure cannot be formatted within the constrained width, a best effort will be made. If compact is false (the default) each item of a long sequence will be formatted on a separate line. If compact is true, as many items as will fit within the width will be formatted on each output line.

Changed in version 3.4: Added the compact parameter.

>>> import pprint
>>> stuff = ['spam', 'eggs', 'lumberjack', 'knights', 'ni']
>>> stuff.insert(0, stuff[:])
>>> pp = pprint.PrettyPrinter(indent=4)
>>> pp.pprint(stuff)
[   ['spam', 'eggs', 'lumberjack', 'knights', 'ni'],
    'spam',
    'eggs',
    'lumberjack',
    'knights',
    'ni']
>>> pp = pprint.PrettyPrinter(width=41, compact=True)
>>> pp.pprint(stuff)
[['spam', 'eggs', 'lumberjack',
  'knights', 'ni'],
 'spam', 'eggs', 'lumberjack', 'knights',
 'ni']
>>> tup = ('spam', ('eggs', ('lumberjack', ('knights', ('ni', ('dead',
... ('parrot', ('fresh fruit',))))))))
>>> pp = pprint.PrettyPrinter(depth=6)
>>> pp.pprint(tup)
('spam', ('eggs', ('lumberjack', ('knights', ('ni', ('dead', (...)))))))

The pprint module also provides several shortcut functions:

pprint.pformat(object, indent=1, width=80, depth=None, *, compact=False)

Return the formatted representation of object as a string. indent, width, depth and compact will be passed to the PrettyPrinter constructor as formatting parameters.

Changed in version 3.4: Added the compact parameter.

pprint.pprint(object, stream=None, indent=1, width=80, depth=None, *, compact=False)

Prints the formatted representation of object on stream, followed by a newline. If stream is None, sys.stdout is used. This may be used in the interactive interpreter instead of the print() function for inspecting values (you can even reassign print = pprint.pprint for use within a scope). indent, width, depth and compact will be passed to the PrettyPrinter constructor as formatting parameters.

Changed in version 3.4: Added the compact parameter.

>>> import pprint
>>> stuff = ['spam', 'eggs', 'lumberjack', 'knights', 'ni']
>>> stuff.insert(0, stuff)
>>> pprint.pprint(stuff)
[<Recursion on list with id=...>,
 'spam',
 'eggs',
 'lumberjack',
 'knights',
 'ni']

pprint.isreadable(object)

Determine if the formatted representation of object is “readable,” or can be used to reconstruct the value using eval(). This always returns False for recursive objects.

>>> pprint.isreadable(stuff)
False
pprint.isrecursive(object)

Determine if object requires a recursive representation.

One more support function is also defined:

pprint.saferepr(object)

Return a string representation of object, protected against recursive data structures. If the representation of object exposes a recursive entry, the recursive reference will be represented as <Recursion on typename with id=number>. The representation is not otherwise formatted.

>>> pprint.saferepr(stuff)
"[<Recursion on list with id=...>, 'spam', 'eggs', 'lumberjack', 'knights', 'ni']"

8.11.1. PrettyPrinter Objects

PrettyPrinter instances have the following methods:

PrettyPrinter.pformat(object)

Return the formatted representation of object. This takes into account the options passed to the PrettyPrinter constructor.

PrettyPrinter.pprint(object)

Print the formatted representation of object on the configured stream, followed by a newline.

The following methods provide the implementations for the corresponding functions of the same names. Using these methods on an instance is slightly more efficient since new PrettyPrinter objects don’t need to be created.

PrettyPrinter.isreadable(object)

Determine if the formatted representation of the object is “readable,” or can be used to reconstruct the value using eval(). Note that this returns False for recursive objects. If the depth parameter of the PrettyPrinter is set and the object is deeper than allowed, this returns False.

PrettyPrinter.isrecursive(object)

Determine if the object requires a recursive representation.

This method is provided as a hook to allow subclasses to modify the way objects are converted to strings. The default implementation uses the internals of the saferepr() implementation.

PrettyPrinter.format(object, context, maxlevels, level)

Returns three values: the formatted version of object as a string, a flag indicating whether the result is readable, and a flag indicating whether recursion was detected. The first argument is the object to be presented. The second is a dictionary which contains the id() of objects that are part of the current presentation context (direct and indirect containers for object that are affecting the presentation) as the keys; if an object needs to be presented which is already represented in context, the third return value should be True. Recursive calls to the format() method should add additional entries for containers to this dictionary. The third argument, maxlevels, gives the requested limit to recursion; this will be 0 if there is no requested limit. This argument should be passed unmodified to recursive calls. The fourth argument, level, gives the current level; recursive calls should be passed a value less than that of the current call.

8.11.2. Example

To demonstrate several uses of the pprint() function and its parameters, let’s fetch information about a project from PyPI:

>>> import json
>>> import pprint
>>> from urllib.request import urlopen
>>> with urlopen('http://pypi.python.org/pypi/Twisted/json') as url:
...     http_info = url.info()
...     raw_data = url.read().decode(http_info.get_content_charset())
>>> project_info = json.loads(raw_data)

In its basic form, pprint() shows the whole object:

>>> pprint.pprint(project_info)
{'info': {'_pypi_hidden': False,
          '_pypi_ordering': 125,
          'author': 'Glyph Lefkowitz',
          'author_email': 'glyph@twistedmatrix.com',
          'bugtrack_url': '',
          'cheesecake_code_kwalitee_id': None,
          'cheesecake_documentation_id': None,
          'cheesecake_installability_id': None,
          'classifiers': ['Programming Language :: Python :: 2.6',
                          'Programming Language :: Python :: 2.7',
                          'Programming Language :: Python :: 2 :: Only'],
          'description': 'An extensible framework for Python programming, '
                         'with special focus\r\n'
                         'on event-based network programming and '
                         'multiprotocol integration.',
          'docs_url': '',
          'download_url': 'UNKNOWN',
          'home_page': 'http://twistedmatrix.com/',
          'keywords': '',
          'license': 'MIT',
          'maintainer': '',
          'maintainer_email': '',
          'name': 'Twisted',
          'package_url': 'http://pypi.python.org/pypi/Twisted',
          'platform': 'UNKNOWN',
          'release_url': 'http://pypi.python.org/pypi/Twisted/12.3.0',
          'requires_python': None,
          'stable_version': None,
          'summary': 'An asynchronous networking framework written in Python',
          'version': '12.3.0'},
 'urls': [{'comment_text': '',
           'downloads': 71844,
           'filename': 'Twisted-12.3.0.tar.bz2',
           'has_sig': False,
           'md5_digest': '6e289825f3bf5591cfd670874cc0862d',
           'packagetype': 'sdist',
           'python_version': 'source',
           'size': 2615733,
           'upload_time': '2012-12-26T12:47:03',
           'url': 'https://pypi.python.org/packages/source/T/Twisted/Twisted-12.3.0.tar.bz2'},
          {'comment_text': '',
           'downloads': 5224,
           'filename': 'Twisted-12.3.0.win32-py2.7.msi',
           'has_sig': False,
           'md5_digest': '6b778f5201b622a5519a2aca1a2fe512',
           'packagetype': 'bdist_msi',
           'python_version': '2.7',
           'size': 2916352,
           'upload_time': '2012-12-26T12:48:15',
           'url': 'https://pypi.python.org/packages/2.7/T/Twisted/Twisted-12.3.0.win32-py2.7.msi'}]}

The result can be limited to a certain depth (ellipsis is used for deeper contents):

>>> pprint.pprint(project_info, depth=2)
{'info': {'_pypi_hidden': False,
          '_pypi_ordering': 125,
          'author': 'Glyph Lefkowitz',
          'author_email': 'glyph@twistedmatrix.com',
          'bugtrack_url': '',
          'cheesecake_code_kwalitee_id': None,
          'cheesecake_documentation_id': None,
          'cheesecake_installability_id': None,
          'classifiers': [...],
          'description': 'An extensible framework for Python programming, '
                         'with special focus\r\n'
                         'on event-based network programming and '
                         'multiprotocol integration.',
          'docs_url': '',
          'download_url': 'UNKNOWN',
          'home_page': 'http://twistedmatrix.com/',
          'keywords': '',
          'license': 'MIT',
          'maintainer': '',
          'maintainer_email': '',
          'name': 'Twisted',
          'package_url': 'http://pypi.python.org/pypi/Twisted',
          'platform': 'UNKNOWN',
          'release_url': 'http://pypi.python.org/pypi/Twisted/12.3.0',
          'requires_python': None,
          'stable_version': None,
          'summary': 'An asynchronous networking framework written in Python',
          'version': '12.3.0'},
 'urls': [{...}, {...}]}

Additionally, maximum character width can be suggested. If a long object cannot be split, the specified width will be exceeded:

>>> pprint.pprint(project_info, depth=2, width=50)
{'info': {'_pypi_hidden': False,
          '_pypi_ordering': 125,
          'author': 'Glyph Lefkowitz',
          'author_email': 'glyph@twistedmatrix.com',
          'bugtrack_url': '',
          'cheesecake_code_kwalitee_id': None,
          'cheesecake_documentation_id': None,
          'cheesecake_installability_id': None,
          'classifiers': [...],
          'description': 'An extensible '
                         'framework for '
                         'Python programming, '
                         'with special '
                         'focus\r\n'
                         'on event-based '
                         'network programming '
                         'and multiprotocol '
                         'integration.',
          'docs_url': '',
          'download_url': 'UNKNOWN',
          'home_page': 'http://twistedmatrix.com/',
          'keywords': '',
          'license': 'MIT',
          'maintainer': '',
          'maintainer_email': '',
          'name': 'Twisted',
          'package_url': 'http://pypi.python.org/pypi/Twisted',
          'platform': 'UNKNOWN',
          'release_url': 'http://pypi.python.org/pypi/Twisted/12.3.0',
          'requires_python': None,
          'stable_version': None,
          'summary': 'An asynchronous '
                     'networking framework '
                     'written in Python',
          'version': '12.3.0'},
 'urls': [{...}, {...}]}